Patients complete a 10-minute questionnaire about factors that might affect changes in breast density at baseline and another questionnaire at 1 year and 2 years post registration. Blood samples are collected at baseline (before initiation of treatment ) and at 1 year post registration for hormone and drug level analysis. Mammograms taken prior to registration (within 12 months prior to enrollment) and at approximately 1 and 2 years post-registration to this study are retrieved and digitized for determination of percent breast density and dense area.